Electrical liquid level control



Feb. 21, 1950 J. M. ANDREWS ELECTRICAL LIQUID LEVEL CONTROL Filed May 10, 1948 SOLENOID VALVE OPEN WHEN ENERGIZED RELAY MAGNET] CALLY OPERATED REVERlNG SWITCH INVENTOR. John M.Andrews ATTORNEYS.

Patented Feb. 21, 1959 ELECTRICAL mourn raver. con'rnor.

John M. Andrews, York, Pa., assixnor to York Corporation, York, Pa., a corporation oi Delaware Application May 10, 1948, Serial No- 26,075

1 Claim. 1

The invention relates to a liquid level responsive means for controlling the supply of liquid to a tank. A typical instance of the need for the invention is a cooling water tank for a condenser in a bus air-conditioning system.

According to the invention a plurality of pairs of electrodes are so located with reference to the tank that when the liquid reaches the desired level in the tank, it will establish an electrical connection between the electrodes of one or more pairs. If the tank tilts about only one axis, two pairs of electrodes would sufllce but in most cases it is desired to control in response to tilt of the tank in any direction and obviously three pairs of electrodes are the minimum number which can be used to define a plane.

The pairs of electrodes are connected in parallel relation with one another in a circuit which includes a source of current and an actuating winding of a relay switch. The switchelement of the relay controls a circuit through a solenoid valve which is interposed in the water supply.

is at the desired depth and the tank is level, the

circuit will be closed through all the pairs of electrodes and the water supply will be cut off. Furthermore, if the liquid level is near tothe desired level but slightly below it and tilt occurs in any direction, the closing of the circuit through some one of the electrodes will cut oil the water supply.

In the preferred embodiment of the invention the solenoid valve is of a type which closes when the solenoid is de-energized and the relay switch is biased to close the solenoid circuit when the relay winding is de-energized as it would normally be when the water level is below the desired depth.

The invention will now be described by reference to the accompanying drawing which shows the invention largely in diagram.

In the drawing the middle pair of electrodes is assumed to be in a plane to the rear of the plane of section of the two outer pairs of electrodes. A portion of the tank appears at l and a corresponding portion of the cover appears at 2. Three pairs of electrodes are shown and since they are identical, the left-hand one will be described. Each pair of electrodes is mounted on an insulating disk 3 bolted to the top 2 of the tank over an aperture 4 through which the electrodes project downwardly into the liquid space in the tank. The outer electrode 5 is a tube fixed in the insulator 8. The inner electrode 6 is mounted within the tube 5 and at a point sub- 2 stantially above the lower end of the tube. It has a stem I threaded in an insulating bushing 8, this construction being adopted to permit the electrode 6 to be adjusted vertically for the purpose of changing the level at which it exercises control. The check nut arrangement indicated generally at 9 is used to lock the stem in its adjusted positions. which permits the escape of air entrapped by liquid rising into the tube.

As stated above, there are three pairs of such electrodes and it may be assumed that when viewed in plan, they are arranged to define an equilateral triangle though such an arrangement is not strictly necessary. Any arrangement by which the three electrodes would define a horizontal plane will suffice.

The pairs of electrodes are connected in parallel relation with one another and are included in a 20 circuit comprising in addition thereto the winding ll of a relay, a source of electric current I! and a magnetically operated reversing switch It. A switch arm I6 is controlled by the winding H. A spring I5 is attached to the switch arm l8 and 26 biases the switch toward its closed position. The

switch arm IG-controls a second circuit by its coaction with the contact l9. When the winding H is energized, the switch arm l6 rests against the back contact [8 which functions simply as a limit stop. The contact I9 is part of a second circuit which comprises the source of electric current l2, a solenoid 20 and a trip coil 2!. The solenoid 20 actuates the inlet valve 22 which controls the flow of liquid to the tank.

The accompanying drawing shows the invention in its non-supplying position. In this position at least one pair of electrodes is in contact with the surface of the liquid in the tank. As long as any pair of electrodes is bridged by the liquid, the first circuit will be completed and the relay winding will be energized. When the liquid level falls to a point where none of the pairs of electrodes is bridged, the winding II will be de-energized and the switch arm [6 and the contact I9 will close, thus energizing the second circuit. The solenoid 20 will open the valve 22, thus supplying liquid to the tank.

As an incident to the energization of the second circuit, the trip coil 2| will operate the reversing switch l3. This results in a reversal of the direction of the current flow across the electrodes, when the liquid again rises to bridge any pair of electrodes. This reversal of the direction of the current will serve to resist incrustation o the electrodes.

The electrode 5 has a vent ll' Although the preierred embodiment is shown in the drawing, it will be obvious that the parts could be arranged so that the inlet valve 22 would be open when the solenoid 20 is de-energized and closed when it is energized. This change would mean that for satisfactory operation of the reversing switch, the trip coil 2| would have to operate to reverse the polarity upon the breaking rather than the making of the second circuit. The embodiment shown is preferable because it insures that no liquid will flow to the tank, ii the source of electric current should fail.

What is claimed is:

Means for controlling the flow of an electrically conductive liquid to a tank to maintain a substantially constant liquid level therein comprising in combination with said tank: a valve controlling the flow of liquid thereto; solenoid means to operate said valve; a plurality of pairs 01' electrodes mounted upon said tank, each pair of electrodes being so located as to be electrically connected by said liquid when the liquid level reaches the desired maximum at that pair of electrodes; a magnetic relay switch having a winding and a switch element to be operated by said winding; an automatic reversing switch comprising a second switch element and a trip coil to operate said second switch element; a first circuit including the winding of the relay 4 switch, said switch element 0! the reversing switch and said pairs 01 electrodes. the latter being connected in parallel with one another; a second circuit including said solenoid, the switch element of the relay switch and said trip coil, said reversing switch being arranged to be actuated by intermittent energization otsaid second circuit and serving to reverse the polarity of the electrodes oi the various pairs whereby incrustation or the electrodes is resisted; and a source of current for said circuits.

JOHN M. ANDREWS.

REFERENCES ('JITED The iollowingreierences are of record in the file of this patent:

UNITED STATES PATENTS 

